Nonpatent Literature 1 discloses a GaN-based light-emitting diode. The GaN-based light-emitting diode is formed on an m-plane GaN substrate. The surface morphology of an n-type GaN layer is improved by an increase in off angle defined in the direction from an m-axis to a c-axis. Nonpatent literature 2 discloses hillocks on an m-plane of an n-type GaN film.
Patent Literature 1 discloses, for example, a semiconductor laser that uses a nonpolar plane (an m-plane or an a-plane) of GaN or InGaN. Patent Literature 2 discloses a light-emitting device in which the effect of the piezoelectric field specific to a GaN-based semiconductor is reduced.    Patent Literature 1: Japanese Patent No. 3816176    Patent Literature 2: U.S. Pat. No. 6,849,472    Nonpatent Literature 1: H. Yamada et. al., CRYS-D-08-00657, UCSB    Nonpatent Literature 2: A. Hirai et. al., Applied Physics Letter, Vol. 91, 191906 (2007)